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J. Biol. Chem., Vol. 280, Issue 7, 6064-6071, February 18, 2005

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Changes in Mg²⁺ Ion Concentration and Heavy Chain Phosphorylation Regulate the Motor Activity of a Class I Myosin^*

Setsuko Fujita-Becker, Ulrike Dürrwang¶, Muriel Erent||, Richard J. Clark**, Michael A. Geeves**, and Dietmar J. Manstein

From the Department of Biophysics, Max-Planck-Institute for Medical Research, Jahnstrasse 29, D-69120 Heidelberg, Germany, the ^**Department of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom, and the Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany

Class I myosins are single-headed motor proteins implicated in various motile processes including organelle translocation, ion channel gating, and cytoskeleton reorganization. Dictyostelium discoideum myosin-ID belongs to subclass 1, whose members are thought to be tuned for rapid sliding. The direct analysis of myosin-ID motor activity is made possible by the production of single polypeptide constructs carrying an artificial lever arm. Using these constructs, we show that the motor activity of myosin-ID is activated 80-fold by phosphorylation at the TEDS site. TEDS site phosphorylation acts by stabilizing the actomyosin complex and increasing the coupling between actin binding and the release of hydrolysis products. A surprising effect of Mg²⁺ ions on in vitro motility was discovered. Changes in the level of free Mg²⁺ ions within the physiological range are shown to modulate motor activity by inhibiting ADP release. Our results indicate that higher concentrations of free Mg²⁺ ions stabilize the tension-bearing actin myosin ADP state and shift the system from the production of rapid movement toward the generation of tension.

Received for publication, November 4, 2004 , and in revised form, November 26, 2004.

^* This work was supported by Deutsche Forschungsgemeinschaft Grants MA1081/5-3 and MA1082/6-1 (to D. J. M.) and Wellcome Trust Grant 070021 (to M. A. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

These authors contributed equally to this work.

^¶ Present address: Marie Curie Research Institute, The Chart, Oxted RH8 OTE Surrey, UK.

^|| Present address: Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany.

To whom correspondence should be addressed: Institut für Biophysikalische Chemie, OE 4350, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany. Tel.: 49-511-5323700; Fax: 49-511-532–5966; E-mail: manstein{at}bpc.mh-hannover.de.

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